Project Summary/Abstract This project focuses on defining the role of transmethylation in the innate and adaptive immune responses relevant to systemic autoimmunity. This is a new area of immunological research that is based on recent studies by us and others showing that inhibition of transmethylation affects normal immune and autoimmune responses. We hypothesize that transmethylation is critical for inflammation and immune responses and that blockade of this post-translational process can curtail systemic autoimmunity. In support of this, we have specifically documented in published and preliminary studies that inhibition of S-adenosyl-L-homocysteine hydrolase (SAHase), a major enzyme involved in transmethylation, leads to immunosuppression by reducing phosphorylation/activation of several key proteins involved in TCR signaling. Strikingly, this effect was noted in CD4, but not CD8 T cells, and correlated with reduced arginine methylation of Vav1. We also documented that stimulation by diverse TLR ligands and the consequent production of inflammatory cytokines was significantly reduced by inhibition of transmethylation. More importantly, treatment of an organ-specific autoimmune mouse model (EAE) and lupus mouse models (MRL-Faslpr and BXSB) with a reversible SAHase inhibitor markedly reduced the incidence, severity, and progression of disease. Here, we propose to perform mechanistic studies to further define the specificity and pathways by which protein methylation affects normal and autoimmune responses with the following three specific aims: 1) determine what PRMT (protein arginine methyltransferase) members are present in T cells, identify the specific PRMT(s) that methylates Vav1 in CD4 T cells, and determine the role of specific PRMTs in T cell, B cell, and macrophage function; 2) define the molecular pathways by which transmethylation inhibition interferes with TLR-dependent and TLR-independent induction of inflammatory mediators by nucleic acids and complexes thereof, thought to be involved in lupus pathogenesis; and 3) characterize the cellular and functional changes that occur due to transmethylation inhibition during disease progression in lupus models. These studies should significantly advance our knowledge of how post-translational modifications affect normal and abnormal immune responses, and have the potential for identifying novel targets for the treatment of autoimmune diseases.